1. Field of the Invention
The present invention relates to the structure of a vehicle subframe, and more particularly, to a vehicle subframe that is integrally provided with a mounting bracket at a top thereof to improve space efficiency so as to allow a double wishbone type suspension to be employed in even compact passenger vehicles.
2. Description of Related Art
As types of independent suspensions, strut type (Macpherson type) and double wishbone type suspensions are widely employed in passenger vehicles.
A strut type suspension has a structure for supporting a vehicle body, in which a strut configured of a shock absorber and a spring is mounted such that the bottom of the strut is mounted on the top of a wheel hub, and a lower arm coupled to a subframe is coupled to the bottom of the wheel hub. While having the advantages of being simple and easy to maintain and repair, and taking up little space on the one hand, the strut type structure is disadvantageous on the other hand by a large amount of frictional force generated by a shock absorber and by providing little lateral support.
A double wishbone type suspension is a structure in which two “V”-shaped (or “Y”-shaped) arms—an upper arm and a lower arm—are mounted on the top and the bottom, respectively, of a wheel hub, and is advantageous in enabling wheel alignment changes or the posture of a vehicle to be relatively freely controlled, and having high rigidity for improved control stability. Specifically, while having the advantages of a relatively greater freedom of design, excellent rigidity, and good vibration insulation, a double wishbone type suspension has the disadvantage of taking up a large amount of space, which limits the use thereof to mostly midsized or larger passenger vehicles.
FIG. 1A illustrates the structure of a double wishbone type suspension in the related art. An upper arm and a lower arm connected to the top and the bottom, respectively, of a wheel hub, have shapes in which ends thereof diverge into two branches to form, as the term “wishbone” suggests, a “V” shape (or a “Y” shape), and the lower arm is mounted from a side direction (a vehicle width direction) of a subframe (mounted at a lower portion of an engine room formed between side members on either side), and the upper arm has a shock absorber to the inside thereof and is mounted to a vehicle body (more specifically, to the upper portion of a side member of the vehicle body disposed to either side of the engine room).
However, an upper arm in a related art double wishbone structure was mounted to a panel portion of a vehicle body so that modularizing the suspension was restrictive and an additional assembly process was required. Further, (in order to prevent excessive changes in camber angle and tread) the length (a) of the upper arm should be provided at a suitable dimension, and in order to secure rigidity at a coupling portion, the upper arm should be mounted to a portion on the vehicle body with high rigidity (for example, on a side member of the vehicle body or nearby), but (because the upper arm tended to be distanced from the side member for the sake of harmonious wheel alignment) the size and the arrangement of the wheel hub is restricted, which leads to the drawback of making it difficult to secure a suitable length for the upper arm.
In addition, when the cross section of a vehicle body side member is enlarged in order to mount the shock absorber or/and enhance the rigidity of the vehicle body, the length of the upper arm can only be further restricted.
As illustrated in FIG. 1B, a structure has been developed in which a shock absorber is disposed lying down along the lengthwise direction of the vehicle body, in order to absorb the magnitude of an impact from a vehicle collision and prevent the front end of the vehicle from diving. In the case of a shock absorber having this arranged structure, the front side of the shock absorber is connected to a bumper mounted on the very front of the vehicle, and the rear side of the shock absorber is mounted in connection through a rocker arm. The rocker arm is in the form of a triangular plate, is mounted on the vehicle body to be capable of pivoting forward and rearward, and has one side thereof connected to the shock absorber and the other side thereof connected to a pushrod connected to the wheel hub.
Accordingly, if the wheel hub is undulated vertically due to impacts from the ground, the pushrod pivots the rocker arm (in the direction indicated by the arrow), and the shock absorber rebounds and bumps along the lengthwise direction of the vehicle body so as to absorb the impact exerted by the pushrod. Further, in the event of a collision to the front of the vehicle, the magnitude of the impact transferred through the bumper is primarily absorbed by the shock absorber, and part of the impact is transferred to the pushrod through the rocker arm and presses on the wheel hub from above so as to raise the front end of the vehicle. This movement of the pushrod counters the tendency of the front end of a vehicle to dive in the event of a vehicle collision and reduces the casualty rate of passengers.
Accordingly, when the above-described impact absorbing structure is applied, the rocker arm and the pushrod should necessarily be provided, leading to further restrictions on the mounting space for the upper arm and the conditions for design requirements.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.